Polythiophenes and devices thereof

ABSTRACT

An electronic device containing a polythiophene  
                 
wherein R represents a side chain, m represents the number of R substituents; A is a divalent linkage; x, y and z represent, respectively, the number of Rm substituted thienylenes, unsubstituted thienylenes, and divalent linkages A, respectively, in the monomer segment subject to z being 0 or 1, and n represents the number of repeating monomer segments in the polymer or the degree of polymerization.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/832,503 filed Apr. 27, 2004, titled “POLYTHIOPHENES AND DEVICESTHEREOF.” That application was a divisional of U.S. application Ser. No.10/042,358, filed Jan. 11, 2002, now U.S. Pat. No. 6,770,904. Bothapplications are hereby fully incorporated by reference.

Reference is also made to U.S. Pat. Nos. 6,949,762; 6,621,099;7,141,644; 6,777,529; and 6,872,801; and to U.S. Ser. No. 10/231,841,filed Aug. 29, 2002, now allowed. These disclosures, all of which aretotally incorporated herein by reference, refer to polythiophenes anddevices thereof. The appropriate components, processes thereof, and usesthereof illustrated in these copending applications may be selected forthe present invention in embodiments thereof.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with the United States Government support underCooperative Agreement No. 70NANBOH3033 awarded by the National Instituteof Standards and Technology (NIST). The United States Government hascertain rights in the invention.

BACKGROUND

The present invention is generally directed to polythiophenes and usesthereof. More specifically, the present invention in embodiments isdirected to a class of polythiophenes wherein certain repeatingthienylene units possess side chains, such as alkyl, which are arrangedin a regioregular manner on the polythiophene backbone, and whichpolythiophenes are, for example, useful as active semiconductivematerials for thin film field-effect transistors (FETs).

Semiconductive polymers like certain polythiophenes, which are useful asactive semiconductor materials in thin film transistors (TFTs), havebeen reported. A number of these polymers have some solubility inorganic solvents and are thus able to be fabricated as semiconductorchannel layers in TFTs by solution processes, such as spin coating,solution casting, dip coating, screen printing, stamp printing, jetprinting and the like. Their ability to be fabricated via commonsolution processes would render their manufacturing simpler and costeffective as compared to the costly conventional photolithographicprocesses typical of silicon-based devices such as hydrogenatedamorphous silicon TFTs. Moreover, desired are transistors fabricatedwith polymer materials, such as polythiophenes, referred to as polymerTFTs, with excellent mechanical durability and structural flexibility,which may be highly desirable for fabricating flexible TFTs on plasticsubstrates. Flexible TFTs would enable the design of electronic deviceswhich usually require structural flexibility and mechanical durabilitycharacteristics. The use of plastic substrates together with organic orpolymer transistor components can transform the traditionally rigidsilicon TFT into a mechanically more durable and structurally flexiblepolymer TFT design. The latter is of particular value to large areadevices such as large-area image sensors, electronic paper and otherdisplay media. Also, the selection of polymer TFTs for integratedcircuit logic elements for low end microelectronics, such as smartcards, radio frequency identification (RFID) tags, and memory/storagedevices, may also greatly enhance their mechanical durability, and thustheir useful life span. Nonetheless, many of the semiconductorpolythiophenes are not, it is believed, stable when exposed to air asthey become oxidatively doped by ambient oxygen, resulting in increasedconductivity. The result is larger off-current and thus lower currenton/off ratio for the devices fabricated from these materials.Accordingly, with many of these materials, rigorous precautions have tobe undertaken during materials processing and device fabrication toexclude environmental oxygen to avoid or minimize oxidative doping.These precautionary measures add to the cost of manufacturing thereforeoffsetting the appeal of certain polymer TFTs as an economicalalternative to amorphous silicon technology, particularly for large areadevices. These and other disadvantages are avoided or minimized inembodiments of the present invention.

REFERENCES

A number of organic semiconductor materials has been described for usein field-effect TFTs, which materials include organic small moleculessuch as pentacene, see for example D. J. Gundlach et al., “Pentaceneorganic thin film transistors—molecular ordering and mobility,” IEEEElectron Device Lett., Vol. 18, p. 87 (1997), to oligomers such assexithiophenes or their variants, see for example reference F. Garnieret al., “Molecular engineering of organic semiconductors: Design ofself-assembly properties in conjugated thiophene oligomers,” Amer. Chem.Soc., Vol. 115, p. 8716 (1993), and certain polythiophenes, such aspoly(3-alkylthiophene), see for example reference Z. Bao et al.,“Soluble and processable regioregular poly(3-hexylthiophene) forfield-effect thin film transistor application with high mobility,” Appl.Phys. Lett. Vol. 69, p. 4108 (1996). Although organic material basedTFTs generally provide lower performance characteristics than theirconventional silicon counterparts, such as silicon crystal orpolysilicon TFTs, they are nonetheless sufficiently useful forapplications in areas where high mobility is not required. These includelarge area devices, such as image sensors, active matrix liquid crystaldisplays and low end microelectronics such as smart cards and RFID tags.TFTs fabricated from organic or polymer materials may be functionallyand structurally more desirable than conventional silicon technology inthe aforementioned areas in that they may offer mechanical durability,structural flexibility, and the potential of being able to beincorporated directly onto the active media of the devices, thusenhancing device compactness for transportability. However, most smallmolecule or oligomer-based devices rely on difficult vacuum depositiontechniques for fabrication. Vacuum deposition is selected primarilybecause the small molecular materials are either insoluble or theirsolution processing by spin coating, solution casting, or stamp printingdo not generally provide uniform thin films. In addition, vacuumdeposition may also involve the difficulty of achieving consistent thinfilm quality for large area format. Polymer TFTs, such as thosefabricated from regioregular polythiophenes of, for example,regioregular poly(3-alkylthiophene-2,5-diyl) by solution processes,while offering some mobility, suffer from their propensity towardsoxidative doping in air. For practical low cost TFT design, it istherefore of value to have a semiconductor material that is both stableand solution processable, and where its performance is not adverselyaffected by ambient oxygen, for example, regioregular polythiophenessuch as poly(3-alkylthiophene-2,5-diyl) are very sensitive to air. TheTFTs fabricated from these materials in ambient conditions generallyexhibit very large off-current, very low current on/off ratios, andtheir performance characteristics degrade rapidly.

References that may be of interest include U.S. Pat. Nos. 6,150,191;6,107,117; 5,969,376; 5,619,357, and 5,777,070.

FIGURES

Illustrated in FIGS. 1 to 4 are various representative embodiments ofthe present invention and wherein polythiophenes are selected as thechannel materials in thin film transistor (TFT) configurations.

SUMMARY AND EMBODIMENTS

It is a feature of the present invention to provide semiconductorpolymers such as polythiophenes, which are useful for microelectronicdevice applications, such as TFT devices.

It is another feature of the present invention to provide polythiopheneswith a band gap of from about 1.5 eV to about 3 eV as determined fromthe absorption spectra of thin films thereof, and which polythiophenesare suitable for use as TFT semiconductor channel layer materials.

In yet a further feature of the present invention there are providedpolythiophenes which are useful as microelectronic components, and whichpolythiophenes have reasonable solubility of, for example, at leastabout 0.1 percent by weight in common organic solvents, such asmethylene chloride, tetrahydrofuran, toluene, xylene, mesitylene,chlorobenzene, and the like, and thus these components can beeconomically fabricated by solution processes such as spin coating,screen printing, stamp printing, dip coating, solution casting, jetprinting, and the like.

Another feature of the present invention resides in providing electronicdevices, such as TFTs with a polythiophene channel layer, and whichlayer has a conductivity of from about 10⁻⁶ to about 10⁻⁹ S/cm(Siemens/centimeter).

Also, in yet another feature of the present invention there are providedpolythiophenes and devices thereof, and which devices exhibit enhancedresistance to the adverse effects of oxygen, that is, these devicesexhibit relatively high current on/off ratios, and their performancedoes not substantially degrade as rapidly as similar devices fabricatedfrom regioregular polythiophenes such as regioregularpoly(3-alkylthiophene-3,5-diyl).

Additionally, in a further feature of the present invention there isprovided a class of polythiophenes with unique structural features whichare conducive to molecular self-alignment under appropriate processingconditions, and which structural features also enhance the stability ofdevice performance. Proper molecular alignment can permit highermolecular structural order in thin films, which can be important toefficient charge carrier transport, thus higher electrical performance.

There are disclosed in embodiments polythiophenes and electronic devicesthereof. More specifically, the present invention relates topolythiophenes illustrated by or encompassed by Formula (I)

wherein, for example, R is a side chain comprising, for example, alkyl,alkyl derivatives, such as alkoxyalkyl; siloxy-subsituted alkyl,perhaloalkyl, such as a perfluoro, polyether, such as oligoethyleneoxide, polysiloxy, and the like; A is a divalent linkage selected, forexample, from the group consisting of arylene such as phenylene,biphenylene, phenanthrenylene, dihydrophenanthrenylene, fluorenylene,oligoarylene, methylene, polymethylene, dialkylmethylene, dioxyalkylene,dioxyarylene, oligoethylene oxide, and the like; m is the number of sidechains, for example 1 or 2; x and y are the numbers of the R substitutedthienylenes and the non-substituted thienylene moieties, respectively;and z is the number of divalent linkages and is usually 0 or 1; therelative positions of the R substituted and non-substituted thienylenemoieties, and the divalent linkage; and n represents the number ofsegments. A in the monomer segment may be different from those presentedin Formula (I), that is for example, polythiophenes (I) schematicallyrepresented by Formula (II) as semiconductor layers in TFT devices:

wherein R is a side chain comprised of, for example, alkyl derivatives,such as alkoxyalkyl, siloxy-subsituted alkyl, perhaloalkyl, such asperfluoro, polyether, such as oligoethylene oxide, polysiloxyderivatives, and the like; a is an integer (or number) of from about 0to about 5; b, c, and d are integers of from about 1 to about 5; and nis the degree of polymerization, and can be from about 5 to over 5,000,and more specifically, from about 10 to about 1,000 wherein the numberaverage molecular weight (M_(n)) of the polythiophenes can be, forexample, from about 2,000 to about 100,000, and more specifically, fromabout 4,000 to about 50,000, and the weight average molecular weight(M_(w)) thereof can be from about 4,000 to about 500,000, and morespecifically, from about 5,000 to about 100,000 both as measured by gelpermeation chromatography using polystyrene standards. Examples of theside chains for the polythiophenes (I) and (II) include alkyl with, forexample, from about 1 to about 25, and more specifically, from about 4to about 12 carbon atoms (included throughout are numbers within therange, for example 4, 5, 6, 7, 8, 9, 10, 11 and 12), such as butyl,pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, isomericforms thereof, mixtures thereof, and the like; alkoxyalkyl with, forexample, from about 2 to about 30 carbon atoms, such as for examplemethoxypropyl, methoxybutyl, methoxyhexyl, methoxyhexyl, methoxyheptyl,and the like, polyether chains, such as polyethylene oxide;perhaloalkyl, such as perfluoroalkyl, polysiloxy chain, such astrialkylsiloxyalkyl derivatives, and the like.

Specific illustrative polythiophenes examples are wherein n is asillustrated herein.

The polythiophenes in embodiments are soluble in common coatingsolvents, for example, in embodiments they possess a solubility of atleast about 0.1 percent by weight, and more specifically, from about 0.5percent to about 5 percent by weight in such solvents as methylenechloride, 1,2-dichloroethane, tetrahydrofuran, toluene, xylene,mesitylene, chlorobenzene, and the like. Moreover, the polythiophenes ofthe present invention in embodiments when fabricated as semiconductorchannel layers in TFT devices provide a stable conductivity of, forexample, from about 10⁻⁹ S/cm to about 10⁻⁶ S/cm, and more specifically,from about 10⁻⁸ S/cm to about 10⁻⁷ S/cm as determined by conventionalfour-probe conductivity measurements. Further, the polythiophenes (II)include side chains that are regioregularly positioned on thepolythiophene backbone, reference Formulas III that follow, and in whichfour polymer chains of polythiophene (II-e) are schematicallyrepresented. The strategically positioned side chains in (II) facilitateproper alignment of side chains which enables formation of higherordered microstructure domains in thin films. It is believed that thesepolythiophenes when fabricated from solutions as thin films of, forexample, about 10 nanometers to about 500 nanometers form closelystacked lamella structures that are conducive to efficient chargecarrier transport. The incorporated unsubstituted thienylene moieties in(II) have some degree of rotational freedom, which helps to disrupt theextended π-conjugation of the polythiophene system to an extent that issufficient to suppress its propensity towards oxidative doping.Accordingly, these materials are more stable in ambient conditions andthe devices fabricated from these polythiophenes are functionally morestable than that of regioregular polythiophenes such as regioregularpoly(3-alkylthiophene-2,5-diyl). When unprotected, the aforementionedstable materials and devices are generally stable for a number of weeksrather than days or hours as is the situation with regioregularpoly(3-alkylthiophene-2,5-diyl) after exposure to ambient oxygen, thusthe devices fabricated from the polythiophenes in embodiments of thepresent invention can provide higher current on/off ratios, and theirperformance characteristics do not substantially change as rapidly asthat of poly(3-alkylthiophene-2,5-diyl) when no rigorous proceduralprecautions have been taken to exclude ambient oxygen during materialpreparation, device fabrication, and evaluation. The polythiophenestability of the present invention in embodiments against oxidativedoping, particularly for low cost device manufacturing, do not usuallyhave to be handled in an inert atmosphere and the processes thereof are,therefore, simpler and more cost effective, and the fabrication thereofcan be applied to large scale production processes.

FORMULAS III

The preparation of polythiophenes of the present invention can beillustrated with reference to the preparation of polythiophene (IV) froma suitably constructed oligothiophene monomer, such as (IIIa) or (IIIb),according to the general processes depicted in Scheme 1. Polythiophene(IV) is a member of polythiophene (II) wherein a=0, b=d=1. Monomer(IIIa) can readily be obtained from the reaction of3-R-thienyl-2-magnesiumbromide with 5,5′-dibromo-2,2′-dithiophene.Monomer (IIIa) or (IIIb) possess side chains which are strategicallyplaced on the terminal thienylene units so that when polymerized theresultant polythiophene (IV) possesses side chains which areregioregularly positioned on its backbone. Unlike the preparation ofregioregular polythiophenes, such as poly(3-alkylthiophene-2,5-diyl)which require regioregular coupling reaction, the polythiophenes of thepresent invention can be prepared by general polymerization techniqueswithout regioregularity complications. Specifically, FeCl₃ mediatedoxidative coupling of (IIIa) has been successfully utilized in thepreparation of polythiophenes (IV).

The polymerization is generally conducted by adding a solution of 1molar equivalent of (IIIa) in a chlorinated solvent, such as chloroform,to a suspension of about 1 to about 5 molar equivalents of anhydrousFeCl₃ in the same chlorinated solvent. The resultant mixture waspermitted to react at a temperature of about 25° C. to about 60° C.under a blanket of dried air or with a slow stream of dried air bubblingthrough the reaction mixture for a period of about 30 minutes to about48 hours. After the reaction, the polymer product can be isolated bywashing the reaction mixture with water or a dilute aqueous hydrochloricacid solution, stirring with a dilute aqueous ammonium solution for aperiod of about 15 minutes to one hour, followed by washing with water,precipitation from a nonsolvent, and optionally extracting thepolythiophene product via soxhlet extraction with appropriate solventssuch as methanol, toluene, xylene, chlorobenzene, and the like. Thepolythiophene product thus obtained can be further purified byprecipitation from a suitable solvent such as methanol or acetone.

Aspects of the present invention relate to an electronic devicecontaining a polythiophene

wherein R represents a side chain, m represents the number of Rsubstituents; A is a divalent linkage; x, y and z represent,respectively, the number of R_(m) substituted thienylenes, unsubstitutedthienylenes, and divalent linkages A, respectively, in the monomersegment subject to z being 0 or 1, and n represents the number ofrepeating monomer segments in the polymer or the degree ofpolymerization; a device which is a thin film transistor (TFT) comprisedof a substrate, a gate electrode, a gate dielectric layer, a sourceelectrode and a drain electrode, and in contact with the source/drainelectrodes and the gate dielectric layer semiconductor a layer comprisedof polythiophene wherein R is alkoxyalkyl, siloxy-subsituted alkyl, aperhaloalkyl, or a polyether; A is a divalent linkage selected from thegroup consisting of arylene of about 6 to about 40 carbon atoms; m is 1or 2; x and y are the number of the R substituted thienylenes and theunsubstituted thienylene moieties, respectively, each of which are from1 to 5; z is zero or 1, and represents the number of divalent linkages;and n represents the number of monomer segments; a device wherein n isfrom about 5 to about 5,000; the number average molecular weight (M_(n))of the polythiophene is from about 2,000 to about 100,000; the weightaverage molecular weight (M_(w)) is from about 4,000 to over 500,000,both M_(w) and M_(n) being measured by gel permeation chromatographyusing polystyrene standards; a device wherein R is alkyl containing from1 to about 20 carbon atoms, and wherein n is from about 10 to about1,000; the M_(n) is from about 4,000 to about 50,000; and the M_(w) isfrom about 5,000 to about 100,000; a device wherein the alkyl side chainR contains from 6 to about 12 carbon atoms; a device wherein the alkylside chain R is butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl,undecyl, or dodecyl; a device wherein the side chain R is aperfluoroalkyl of about 2 to about 15 carbon atoms; a device wherein theside chain R is siloxyalkyl of trimethylsiloxyalkyl,triethylsiloxyalkyl, and wherein alkyl optionally contains from about 4to about 10 carbons, and which alkyl is butyl, pentyl, hexyl, heptyl, oroctyl; a device wherein the divalent linkage A is an arylene with fromabout 6 to about 40 carbon atoms; a TFT device wherein the divalentlinkage A is selected from the group consisting of phenylene,biphenylene, phenanthrenylene, 9,1 0-dihydrophenanthrenylene,fluorenylene, methylene, polymethylene, dioxyalkylene, dioxyarylene, andoligoethylene oxide; a thin film transistor containing saidpolythiophene is represented by

wherein R is a side chain; a, b, c, and d represent the number ofthienylene moieties; and n is the degree of polymerization; a devicewherein R is alkyl containing from about 1 to about 20 carbon atoms; adevice wherein R is alkyl containing from about 6 to about 12 carbonatoms; a device wherein R is butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, or dodecyl; a device wherein b and d are from about 1 toabout 5; a device wherein b and d are from about 1 to about 3; a devicewherein a is from about 0 to about 5, and c is about 1 to about 5, orwherein a is about 0 to about 3, and c is about 1 to about 3; a thinfilm transistor containing a polythiophene represented by Formula (IV)

a thin film transistor device containing a polythiophene selected fromthe group consisting of polythiophenes (II-a) through (II-o)

a thin film transistor containing a polythiophene selected from thegroup consisting of (II-a) through (II-e)

a thin film transistor containing a polythiophene selected from thegroup consisting of (II-a) through (II-e)

a device wherein n is a number of from about 5 to about 5,000; a devicewherein n is a number of from about 5 to about 3,000; a device wherein nis a number of from about 5 to about 5,000; a device wherein R is hexyl,heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, orpentadecyl, and the like; and m=1, x=y=2, z=0 or 1; a device wherein Ris hexyl, heptyl, octyl, octyl, nonyl, decyl, undecyl, dodecyl,tridecyl, tetradecyl, or pentadecyl, and m=1, x=y=2, and z=0 or 1; adevice wherein the polythiophene selected possesses a M_(n) of fromabout 2,000 to about 100,000, and a M_(w) of from about 4,000 to about500,000; a device wherein the polythiophene possesses a M_(n) of fromabout 2,000 to about 100,000, and a M_(w) of from about 4,000 to about1,000,000; a device wherein the polythiophene is selected from the groupconsisting of (II-a) through Formula (II-e), and wherein n is a numberof from about 50 to about 3,000

a TFT device wherein the substrate is a plastic sheet of a polyester, apolycarbonate, or a polyimide; the gate source and drain electrodes areeach independently comprised of gold, nickel, aluminum, platinum, indiumtitanium oxide, or a conductive polymer, and the gate is a dielectriclayer comprised of silicon nitride or silicon oxide; a TFT devicewherein the substrate is glass or a plastic sheet; said gate, source anddrain electrodes are each comprised of gold, and the gate dielectriclayer is comprised of the organic polymer poly(methacrylate), orpoly(vinyl phenol); a device wherein the polythiophene layer is formedby solution processes of spin coating, stamp printing, screen printing,or jet printing; a device wherein the gate, source and drain electrodes,the gate dielectric, and semiconductor layers are formed by solutionprocesses of spin coating, solution casting, stamp printing, screenprinting, or jet printing; and a TFT device wherein the substrate is aplastic sheet of a polyester, a polycarbonate, or a polyimide, and thegate, source and drain electrodes are fabricated from the organicconductive polymer polystyrene sulfonate-doped poly(3,4-ethylenedioxythiophene) or from a conductive ink/paste compound of a colloidaldispersion of silver in a polymer binder, and the gate dielectric layeris organic polymer or inorganic oxide particle-polymer composite; deviceor devices include electronic devices such as TFTs.

DESCRIPTION OF THE FIGURES

In FIG. 1 there is schematically illustrated a TFT configuration 10comprised of a substrate 16, in contact therewith a metal contact 18(gate electrode), and a layer of an insulating dielectric layer 14 withthe gate electrode having a portion thereof or the entire gate incontact with the dielectric layer 14 with the gate electrode having aportion thereof or the entire gate in contact with the dielectric layer14 on top of which layer 14 two metal contacts, 20 and 22 (source anddrain electrodes), are deposited. Over and between the metal contacts 20and 22 is the polythiophene semiconductor layer 12. The gate electrodecan be included in the substrate, in the dielectric layer, and the likethroughout.

FIG. 2 schematically illustrates another TFT configuration 30 comprisedof a substrate 36, a gate electrode 38, a source electrode 40, and adrain electrode 42, an insulating dielectric layer 34, and thepolythiophene semiconductor layer 32.

FIG. 3 schematically illustrates a further TFT configuration 50comprised of a heavily n-doped silicon wafer 56, which can act as a gateelectrode, a thermally grown silicon oxide dielectric layer 54, thepolythiophene semiconductor layer 52, on top of which are deposited asource electrode 60 and a drain electrode 62; and a gate electrodecontact 64.

FIG. 4 schematically illustrates a TFT configuration 70 comprised ofsubstrate 76, a gate electrode 78, a source electrode 80, a drainelectrode 82, the polythiophene semiconductor layer 72, and aninsulating dielectric layer 74.

Also, other devices not disclosed, especially TFT devices, areenvisioned, reference for example known TFT devices.

In some embodiments of the present invention, an optional protectinglayer may be incorporated on top of each of the transistorconfigurations of FIGS. 1, 2, 3 and 4. For the TFT configuration of FIG.4, the insulating dielectric layer 74 may also function as a protectinglayer.

In embodiments and with further reference to the present invention andthe Figures, the substrate layer may generally be a silicon materialinclusive of various appropriate forms of silicon, a glass plate, aplastic film or a sheet, and the like depending on the intendedapplications. For structurally flexible devices, a plastic substrate,such as for example polyester, polycarbonate, polyimide sheets, and thelike, may be selected. The thickness of the substrate may be, forexample, from about 10 micrometers to over 10 millimeters with aspecific thickness being from about 50 to about 100 micrometersespecially for a flexible plastic substrate and from about 1 to about 10millimeters for a rigid substrate such as glass or silicon.

The insulating dielectric layer, which can separate the gate electrodefrom the source and drain electrodes, and in contact with thesemiconductor layer, can generally be an inorganic material film, anorganic polymer film, or an organic-inorganic composite film. Thethickness of the dielectric layer is, for example, from about 10nanometers to about 1 micrometer with a more specific thickness beingabout 100 nanometers to about 500 nanometers. Illustrative examples ofinorganic materials suitable as the dielectric layer include siliconoxide, silicon nitride, aluminum oxide, barium titanate, bariumzirconate titanate, and the like; illustrative examples of organicpolymers for the dielectric layer include polyesters, polycarbonates,poly(vinyl phenol), polyimides, polystyrene, poly(methacrylate)s,poly(acrylate)s, epoxy resin, and the like; and illustrative examples ofinorganic-organic composite materials include nanosized metal oxideparticles dispersed in polymers such as polyester, polyimide, epoxyresin and the like. The insulating dielectric layer is generally of athickness of from about 50 nanometers to about 500 nanometers dependingon the dielectric constant of the dielectric material used. Morespecifically, the dielectric material has a dielectric constant of, forexample, at least about 3, thus a suitable dielectric thickness of about300 nanometers can provide a desirable capacitance, for example, ofabout 10⁻⁹ to about 10⁻⁷ F/cm².

Situated, for example, between and in contact with the dielectric layerand the source/drain electrodes is the active semiconductor layercomprised of the polythiophenes illustrated herein, and wherein thethickness of this layer is generally, for example, about 10 nanometersto about 1 micrometer, or about 40 to about 100 nanometers. This layercan generally be fabricated by solution processes such as spin coating,casting, screen, stamp, or jet printing of a solution of thepolythiophenes of the present invention.

The gate electrode can be a thin metal film, a conducting polymer film,a conducting film generated from a conducting ink or paste, or thesubstrate itself (for example heavily doped silicon). Examples of gateelectrode materials include but are not limited to aluminum, gold,chromium, indium tin oxide, conducting polymers, such as polystyrenesulfonate-doped poly(3,4-ethylenedioxythiophene) (PSS/PEDOT), aconducting ink/paste comprised of carbon black/graphite or colloidalsilver dispersion contained in a polymer binder, such as ELECTRODAGavailable from Acheson Colloids Company and silver filled electricallyconductive thermoplastic ink available from Noelle Industries, and thelike. The gate layer can be prepared by vacuum evaporation, sputteringof metals or conductive metal oxides, coating from conducting polymersolutions or conducting inks or dispersions by spin coating, casting orprinting. The thickness of the gate electrode layer is, for example,from about 10 nanometers to about 10 micrometers, and a specificthickness is, for example, from about 10 to about 200 nanometers formetal films and about 1 to about 10 micrometers for polymer conductors.

The source and drain electrode layer can be fabricated from materialswhich provide a low resistance ohmic contact to the semiconductor layer.Typical materials suitable for use as source and drain electrodesinclude those of the gate electrode materials such as gold, nickel,aluminum, platinum, conducting polymers, and conducting inks. Typicalthickness of this layer is about, for example, from about 40 nanometersto about 1 micrometer with the more specific thickness being about 100to about 400 nanometers. The TFT devices contain a semiconductor channelwith a width W and length L. The semiconductor channel width may be, forexample, from about 10 micrometers to about 5 millimeters, with aspecific channel width being about 100 micrometers to about 1millimeter. The semiconductor channel length may be, for example, fromabout 1 micrometer to about 1 millimeter with a more specific channellength being from about 5 micrometers to about 100 micrometers.

The source electrode is grounded and a bias voltage of generally, forexample, about 0 volt to about −80 volts is applied to the drainelectrode to collect the charge carriers transported across thesemiconductor channel when a voltage of generally about +10 volts toabout −80 volts is applied to the gate electrode.

Other known materials not recited herein for the various components ofthe TFT devices of the present invention can also be selected inembodiments.

The following Examples are provided.

GENERAL PROCEDURE

a) Device Fabrication:

There was selected a top-contact thin film transistor configuration asschematically illustrated, for example, in FIG. 3.

The test device was comprised of an n-doped silicon wafer with athermally grown silicon oxide layer of a thickness of about 110nanometers thereon. The wafer functioned as the gate electrode while thesilicon oxide layer acted as the gate dielectric and had a capacitanceof about 32 nF/cm² (nanofarads/square centimeter). The fabrication ofthe device was accomplished at ambient conditions without anyprecautions to exclude the materials and device from exposure to ambientoxygen, moisture, or light. The silicon wafer was first cleaned withmethanol, air dried, and then immersed in a 0.01 M solution of1,1,1,3,3,3-hexamethyidisilazane in dichloromethane for 30 minutes atroom temperature, about 23° C. to about 25° C. Subsequently, the waferwas washed with dichloromethane and dried. The test semiconductorpolythiophene layer of about 30 nanometers to 100 nanometers inthickness was then deposited on top of the silicon oxide dielectriclayer by spin coating at a speed of 1,000 rpm for about 35 seconds, anddried in vacuo at 80° C. for 20 hours. The solution used in fabricatingthe semiconductor layer was comprised of 1 percent by weight of thepolythiophene in an appropriate solvent, and was filtered through a 0.45μm filter before use. Thereafter, the gold source and drain electrodeswere deposited on top of the semiconductor polythiophene layer by vacuumdeposition through a shadow mask with various channel lengths andwidths, thus creating a series of transistors of various dimensions. Forconsistency, the devices after fabrication were kept in a dry atmosphereof about 30 percent relative humidity in the dark before and afterevaluation.

b) TFT Device Characterization:

The evaluation of field-effect transistor performance was accomplishedin a black box at ambient conditions using a Keithley 4200 SCSsemiconductor characterization system. The carrier mobility, μ, wascalculated from the data in the saturated regime (gate voltage,V_(G)<source-drain voltage, V_(SD)) according to equation (1)I _(SD) =C _(i)μ(W/2L)(V _(G) −V _(T))²  (1)where I_(SD) is the drain current at the saturated regime, W and L are,respectively, the semiconductor channel width and length, Ci is thecapacitance per unit area of the gate dielectric layer, and V_(G) andV_(T) are, respectively, the gate voltage and threshold voltage. V_(T)of the device was determined from the relationship between the squareroot of I_(SD) at the saturated regime and V_(G) of the device byextrapolating the measured data to I_(SD)=0.

Another property of field-effect transistor is its current on/off ratio.This is the ratio of the saturation source-drain current when the gatevoltage V_(G) is equal to or greater than the drain voltage V_(D) to thesource-drain current when the gate voltage V_(G) is zero.

COMPARATIVE EXAMPLE

A series of comparative thin film transistors were fabricated with theknown regioregular polythiophene, poly(3-hexythiophene-2,5-diyl), whichis commonly known as P3HT. This material was purchased from AldrichChemical and was purified by three successive precipitations of itssolution in chlorobenzene from methanol.

The devices were fabricated in ambient conditions in accordance with theabove procedure. Using transistors with a dimension of W=5,000 μm andL=60 μm, the following average properties from at least five transistorswere obtained: Mobility: 1 to 1.2 × 10⁻² cm²/V · sec Initial on-offratio: 1.5 to 2.1 × 10³ On-off ratio after 5 days: 5 to 10

The observed low initial current on/off ratios are an indication of thepropensity of poly(3-hexythiophene-2,5-diyl) towards oxidative doping,that is the instability of poly(3-hexythiophene-2,5-diyl) in thepresence of ambient oxygen. The drastic reductions in the current on/offratios over just a five-day period further confirm the functionalinstability of poly(3-hexythiophene-2,5-diyl) in ambient conditions.

EXAMPLE (a) Synthesis ofPoly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene](IIe)

The monomer 5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene for thepreparation of (IIe) was synthesized as follows:

A solution of 2-bromo-3-dodecylthiophene (11.5 grams, 34.92 mmol) in 40milliliters of anhydrous tetrahydrofuran (THF) was added slowly over aperiod of 20 minutes to a mechanically stirred suspension of magnesiumturnings (1.26 grams, 51.83 mmol) in 10 milliliters of THF(tetrahydrofuran) in a 100 milliliter round-bottomed flask under aninert argon atmosphere. The resultant mixture was stirred at roomtemperature of about 22° C. to 25° C. for 2 hours, and then at 50° C.for 20 minutes before cooling down to room temperature. The resultantmixture was then added via a cannula to a mixture of5,5′-dibromo-2,2′-dithiophene (4.5 grams, 13.88 mmol) and[1,3-bis(diphenylphosphino]dichloronickel (II) (0.189 gram, 0.35 mmol)in 80 milliliters of anhydrous THF in a 250 milliliter round-bottomedflask under an inert atmosphere, and refluxed for 48 hours.Subsequently, the reaction mixture was diluted with 200 milliliters ofethyl acetate, was washed twice with water and with a 5 percent aqueoushydrochloric acid (HCl) solution, and dried with anhydrous sodiumsulfate. A dark brown syrup, obtained after evaporation of the solvent,was purified by column chromotography on silica gel yielding5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene as a yellow crystallineproduct in 55 percent yield, m.p. 58.9° C.

The NMR spectrum of the above obtained compound was recorded at roomtemperature using a Bruker DPX 300 NMR spectrometer:

¹H NMR (CDCl₃):δ 7.18 (d, J=5.4 Hz, 2H), 7.13 (d, J=3.6 Hz, 2H), 7.02(d, J=3.6 Hz, 2H), 6.94 (d, J=5.4 Hz, 2H), 2.78 (t, 4H), 1.65 (q, 1.65,4H), 1.28 (bs, 36H), 0.88 (m, 6H).

The polymerization of 5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene wasachieved by the FeCl₃-mediated oxidative coupling reaction as follows:

A solution of 5,5′-bis(3-dodecyl-2-thienyl)-2,2′-dithiophene (0.50 gram,0.75 mmol) in 7 milliliters of chloroform was added slowly over a periodof about 10 minutes to a well stirred mixture of FeCl₃ (0.40 gram, 2.47mmol) in 3 milliliters of chloroform in a 50 milliliter round-bottomedflask in a dry atmosphere. The resultant mixture was heated at 50° C.for 1 hour, then 40° C. for 24 hours under a blanket of dry air. Afterthe polymerization, the mixture was diluted with 20 milliliters oftoluene and washed three times with water. The separated organic phasewas stirred with 200 milliliters of 7.5 percent of an aqueous ammoniasolution for half an hour, washed three times with water, and thenpoured into methanol to precipitate the crude polythiophene product. Thelatter was purified by soxhlet extraction with methanol, hexane, andchlorobenzene, M_(w) 27,300; M_(n) 16,900 relative to polystyrenestandards.

Thin film transistor devices were fabricated as indicated herein usingthe following polythiophenes by spin coating a 1 percent by weightsolution of a polythiophene in chlorobenzene and drying in vacuo at 80°C. for 20 hours. No precautions were taken to exclude ambient oxygen,moisture or light during device fabrication. Using the transistors withdimension of W=5,000 μm and L=60 μm, the following average propertiesfrom at least five separate transistors for each polythiophene aresummarized in Table 1. TABLE 1 Current PolythiopheneReaction/Purification Mobility Initial Current On/Off Ratio (IIe) M_(w)(M_(n)) Conditions (Cm²/V · Sec) On/Off Ratio After 5 Days 3,890 (3,880)25° C. (24 hours); 0.9-2.0 × 10⁻⁴ 1.2 × 10³ — Precipitated from methanol14,900 (9,000) 40° C. (1 hour), then 25° C. 2.0-3.1 × 10⁻⁴ 2.2-4.7 × 10³— (48 hours); Extracted with toluene 14,900 (9,000) 40° C. (1 hour),then 25° C. 1.1-3.4 × 10⁻³ 4.5-9.0 × 10⁴ 0.7-1.1 × 10⁴ Device 2 further(48 hours); Extracted with annealed at toluene 135° C. for 10 min 19,000(11,400) 40° C. (24 hours), then 1.9-8.7 × 10⁻³ 5.0-8.5 × 10⁵ 1.0-2.5 ×10⁵ 25° C. (24 hours); Extracted with methanol, hexane, thenchlorobenzene 27,300 (16,900) 50° C. (1 hour), then 40° C. 0.9-2.0 ×10⁻² 1.0-5.1 × 10⁶ 1.9-3.2 × 10⁵ (24 hours); Extracted with methanol,hexane, then chlorobenzene

Further, the average current on/off ratio for the devices using theinvention polythiophene with a M_(w) of 27,300 after 40 days was, forexample, about 1×10⁵.

The stability of the polythiophene semiconductor layer of the presentinvention was demonstrated, for example, by the high initial currenton/off ratios and the slow reductions in the current on/off ratios ofthe devices.

Other embodiments and modifications of the present invention may occurto those skilled in the art subsequent to a review of the informationpresented herein; these embodiments and modifications, equivalentsthereof, substantial equivalents thereof, or similar equivalents thereofare also included within the scope of this invention.

1. An electronic device containing a regioregular polythiophene

wherein R represents a side chain, m represents the number of Rsubstituents; A is a divalent linkage; x, y and z represent,respectively, the number of R_(m) substituted thienylenes, unsubstitutedthienylenes, and divalent linkages A in the monomer segment subject to zbeing 0 or 1, and n represents the number of repeating monomer segmentsin the polymer or the degree of polymerization, and which device iscomprised of a substrate, a gate electrode, a gate dielectric layer, asource electrode and a drain electrode, and in contact with thesource/drain electrodes and optionally the gate dielectric layer asemiconductor layer comprised of said polythiophene wherein R is analkyl, alkoxyalkyl, siloxy-substituted alkyl, a perhaloalkyl, or apolyether; A is a divalent linkage comprising from about 1 to about 40carbon atoms; m is 1 or 2; x and y are the number of the R substitutedthienylenes and the unsubstituted thienylene moieties, respectively,each of which are from 1 to 5; z is zero or 1, and represents the numberof divalent linkages; and n represents the number of monomer segments.2. A device in accordance with claim 1 wherein said polythiophene isrepresented by

wherein R is a side chain; a, b, c, and d represent the number ofthienylene moieties; and n is the degree of polymerization.
 3. A devicein accordance with claim 2 wherein said polythiophene is represented byFormula (IV)


4. A device in accordance with claim 1 wherein said substrate is aplastic sheet of a polyester, a polycarbonate, or a polyimide; saidgate, source, and drain electrodes are each independently comprised ofgold, nickel, aluminum, platinum, indium titanium oxide, or a conductivepolymer, and said gate is a dielectric layer comprised of siliconnitride or silicon oxide.
 5. A device in accordance with claim 1 whereinsaid substrate is glass or a plastic sheet; said gate, source and drainelectrodes are each comprised of gold, and said gate dielectric layer iscomprised of the organic polymer poly(methacrylate), or poly(vinylphenol).
 6. A device in accordance with claim 1 wherein saidpolythiophene layer is formed by solution processes of spin coating,stamp printing, screen printing, or jet printing.
 7. A device inaccordance with claim 1 wherein said gate, source and drain electrodes,said gate dielectric, and semiconductor layers are formed by solutionprocesses of spin coating, solution casting, stamp printing, screenprinting, or jet printing.
 8. A device in accordance with claim 1wherein the substrate is a plastic sheet of a polyester, apolycarbonate, or a polyimide, and the gate, source and drain electrodesare fabricated from the organic conductive polymer polystyrenesulfonate-doped poly(3,4-ethylene dioxythiophene) or from a conductiveink/paste compound of a colloidal dispersion of silver in a polymerbinder, and the gate dielectric layer is organic polymer or inorganicoxide particle-polymer composite.